An information network, e.g. the Internet (or more particularly the World Wide Web hosted thereon), facilitates delivery of content from content providers to content recipients. A content provider, e.g., a person or company, may provide content for display on a web page or other document. Presentation of the content may include text, video, audio, an interactive element, and/or any combination thereof. The presentation may include content from multiple content providers. For example, the presentation may include third party advertisements displayed on a web page together with information from another content provider. A person viewing a web page rendered by a client device may see content from multiple providers in a single web page or during a single web browsing session.
In addition to presenting content, web pages may also be used to submit information or queries to data servers. An example is a user-entered search for information. A user's search may invoke keywords indicating the user's interests. Content providers may wish to identify a set of keywords and to associate a particular content item with the set of keywords for delivery to the user.